Middle English word halou comes from Old English hē, Old English ēalā, Old English lā, and later Old English eala (Oh!, alas!.)

Detailed word origin of halou

Dictionary entry	Language	Definition
hē	Old English (ang)
ēalā	Old English (ang)
lā	Old English (ang)
eala	Old English (ang)	Oh!, alas!.
halloo	Middle English (enm)

Words with the same origin as halou